This invention relates generally to on-board systems and methods for detecting fuel vapor leakage from an evaporative emission space of an automotive vehicle fuel system, relating particularly to a leak verification system characterized by various novel aspects one of which comprises selectively communicating evaporative emission space cooperatively defined by a fuel tank and a vapor storage canister through a purge valve to an intake system of an engine in different ways provide various novel test capabilities.
A known on-board evaporative emission control system for an automotive vehicle comprises a vapor collection canister that collects volatile fuel vapors generated in the headspace of the fuel tank by the volatilization of liquid fuel in the tank and a purge valve for periodically purging fuel vapors to the intake system of the engine. The fuel tank headspace and the vapor collection canister define most of the volume of an evaporative emission space where fuel vapors are contained so they do not escape to atmosphere. Known purge valves are sometimes referred to by various names that include canister purge solenoid (CPS) valves and proportional purge solenoid (PPS) valves. Certain purge valves are electrically controlled. Such a purge valve may comprise a solenoid actuator that is under the control of a microprocessor-based engine management system, sometimes referred to by various names, such as an engine management computer or an engine electronic control unit, to control the opening and closing of the purge valve and hence control flow from the evaporative emission space to the engine intake system.
During conditions conducive to purging, the evaporative emission space is purged to the engine intake system through the purge valve. The space is vented to atmosphere by opening the vent valve, and the purge valve is opened by a signal from the engine management computer in an amount that allows vacuum developed in the engine intake system by operation of the engine to draw fuel vapors that are present in the tank headspace and/or stored in the canister for entrainment with combustible mixture passing into the engine""s combustion chamber space at a rate consistent with engine operation so as to provide both acceptable vehicle driveability and an acceptable level of tailpipe emissions.
Certain governmental regulations require that certain automotive vehicles powered by internal combustion engines which operate on volatile fuels such as gasoline, have evaporative emission control systems equipped with an on-board diagnostic capability for determining if a leak is present in the evaporative emission space. It has heretofore been proposed to make such a determination by temporarily creating a pressure condition in the evaporative emission space that is substantially different from the ambient atmospheric pressure, and then watching for a change in that substantially different pressure which is indicative of a leak.
It is believed fair to say that there are two basic types of diagnostic systems and methods for determining integrity of an evaporative emission space against leakage.
Commonly owned U.S. Pat. No. 5,146,902 xe2x80x9cPositive Pressure Canister Purge System Integrity Confirmationxe2x80x9d discloses one type: namely, a system and method for making a leakage determination by pressurizing the evaporative emission space to a certain positive pressure therein (the word xe2x80x9cpositivexe2x80x9d meaning relative to ambient atmospheric pressure) and then watching for a drop in positive pressure indicative of a leak. Other positive pressure type systems are disclosed in other commonly owned patents, including U.S. Pat. Nos. 5,383,437; and 5,474,050.
The other of the two general types of systems for making a leakage determination does so by creating in the evaporative emission space a certain negative pressure (the word xe2x80x9cnegativexe2x80x9d meaning relative to ambient atmospheric pressure so as to denote vacuum) and then watching for a loss of vacuum indicative of a leak. A known procedure employed by this latter type of system in connection with a leak test comprises utilizing engine manifold vacuum to create vacuum in the evaporative emission space. Because that space may, at certain non-test times, be vented through the canister to allow vapors to be efficiently purged when the purge valve is opened for purging fuel vapors from the tank headspace and canister, it is known to communicate the canister vent port to atmosphere through the open vent valve when vapors are being purged to the engine. The vent valve however closes preparatory to a leak test so that a desired test vacuum can be drawn in the evaporative emission space for the test. Once a desired vacuum has been drawn, the purge valve is closed, and leakage appears as a loss of vacuum during the length of the test time after the purge valve has been operated closed.
In order for an engine management computer to ascertain when a desired vacuum has been drawn so that it can command the purge valve to close, and for loss of vacuum to thereafter be detected, it is known to employ an electric sensor, or transducer, that measures negative pressure, i.e. vacuum, in the evaporative emission space by supplying a measurement signal to the engine management computer. It is known to mount a pressure sensor in various ways. One way is on the vehicle fuel tank where the sensor is exposed to the tank headspace, as in commonly owned U.S. Pat. No. 5,267,470 disclosing a pressure sensor mounting in conjunction with a fuel tank roll-over valve. Another way is described in commonly owned U.S. Pat. No. 6,050,245 disclosing a pressure sensor mounting in a vent valve. Other commonly owned patents such as U.S. Pat. Nos. 5,957,115; 5,967,124; 6,009,746; 6,016,690; 6,016,691; 6,016,793; and 6,044,314 disclose various leak detection systems some of which include modules containing both a pressure sensor and a vent valve.
One generic aspect of the present invention relates to an automotive vehicle that is powered by an internal combustion engine and comprises a tank for storing volatile fuel that is consumed by the engine and a vapor storage canister that comprises a dirty air port in communication with headspace of the tank to cooperatively define an evaporative emission space for containing vapor generated by the evaporation of liquid fuel in the tank and that comprises a vapor absorbent medium separating the dirty air port from a clean air port. A system performs a leak verification test to test the evaporative emission space for leakage comprising self-calibrating the purge valve, closing the evaporative emission space to atmosphere and an intake system of the engine and monitoring for conditions calling for aborting the test, performing a leak determination test, and entering a sleep mode while the engine continues to run.
Another generic aspect of the present invention relates to the method performed by the above-described system.
The foregoing, and other features and aspects, along with various advantages and benefits of the invention, will be seen in the ensuing description and claims, which are accompanied by drawings. The drawings, which are incorporated herein and constitute part of this specification, disclose a preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.